Myocardial infarction (MI) is a leading cause of mortality in today's society. Injury to myocardium is a manifestation of the intrinsic cellular response to ischemia and of an extrinsic acute inflammation. Recent pre-clinical studies have revealed that pre-existing natural IgM functions as the critical mediator between the intrinsic and extrinsic responses in injury induction. The goal of this proposal is to expand these novel basic science discoveries at the clinical level. Knowledge gained from this study will provide a new basis for clinical management of myocardial infarction. The specific aims are as follows: Aim 1. To determine whether natural IgM antibodies against an ischemia-specific self antigen (non-muscle myosin heavy chain II, NMHC-II) are present in normal individuals and patients with acute myocardial infarction. Aim 2. To investigate whether the levels of these autoimmune antibodies correlate with the degrees of myocardial injury. PUBLIC HEALTH RELEVANCE This study will provide important insight of a new mechanism in ischemic myocardial injury, and may identify new markers for myocardial infarction.